HELP!!! Tenant requesting ANOTHER move out extension!

[Matt Romano]

I purchased my first 2-family home this past July. its an up / down 2 unit that I will "house hack". The upstairs tenant (unit where I'll live) received a notice to vacate from me back in July, stating that she had until the end of September to hand over the keys. I got a letter back from her within a week stating that she would be out before my requested date; by the end of August. This was good news as I would be able to start some renovating to my unit sooner, and thus obviously move in quicker.  As the end of August came closer, I received an e-mail from her asking if I could go back to my original request and allow her to stay for the month of September.  I decided that that wasn't an issue because of two main reasons: 1. I was in the middle of doing some construction on the detached 3 car garage, and needed at least another month to reach full completion there, and 2. Another month of rent sounded good to me, lol. 

So here we are, nearing the end of the month that she's supposed to be out, and I get an email from her this afternoon, explaining how her new apartment isn't ready to be moved into yet.  And requesting just ONE more WEEK in order to transition smoothly into her new place.  I understand completely that I do not have to cater to her wants, and that by allowing her the additional week I am enabling her. I agree with all of those whom I can already hear through the computer about treating this like a business, and not a hobby.  However, I am STILL not finished with the garage, and an additional week or 2 wouldn't bother me much in terms of my timeframe. I am leaning towards allowing an additional week or 2 that way I can finish up what I need to with the garage and not be overwhelmed with both the garage and unit renovations at the same time, as I'm doing nearly all of it DIY style. 

Can I have her stay for 2 weeks for an amount that I come up with thats MORE than just 1/2 the months rent (say as like, an inconvenience fee), If both her and I agree and sign papers stating so.  For example, her current rent is $675/mo, and if I charged $400 for two weeks.  

Or should I just require another full months rent (regardless if she really needs just a week) and risk delaying my schedule back a full month.  Or would I legally have to prorate accurately if we both signed a new date for her to be out?

And what are your thoughts on this matter as a whole? have any of you dealt with similar situations? Sorry for such a long post! I appreciate all your comments in advance as always

-Matt